Many conventional ball-point pens include an ink containing "writing tube" or refill which is normally retracted within the casing of the pen and which can be extended to expose the pen point when the pen is to be used. A number of different types of mechanisms are used for this purpose. Perhaps the most common of these includes a push-button located at the non-writing end of the pen which is depressed to cause an extending movement of the refill tube and a catch, which is released when the push-button is depressed, and cooperates with a spring to enable the refill tube to be retracted.
A retractable ball-point pen mechanism of particular interest here is that disclosed in U.S. Pat. No. 3,315,643 (Eratico). The mechanism in question includes a hollow tubular casing which is open at one end to permit the point of the refill tube to be extended therethrough and a impeller, including a helical cam surface, which is rotatably mounted within the casing and which engages the other end of the refill and, when rotated, causes axial movement of the refill tube. The casing includes a barrel portion and cap portion, the impeller being located within the cap portion. The refill tube is mounted within the casing with the aid of a bushing which is fixed within the cap portion, the refill extending through an axial aperture in the bushing which is offset with respect to the longitudinal axis of the bushing. The impeller is affixed to a small knob located at the non-writing end of the casing so that rotation of the knob causes rotation of the impeller and thereby produces axial movement of the refill tube. A spring biases the non-writing end of the refill tube against the cam surface of the impeller so that rotation of the control knob in a first direction causes the writing end of the refill tube to be extended beyond the end of the casing so that the pen can be used to write and rotation of the knob in the opposite direction causes the refill to be retracted within the casing.
Although the writing implement disclosed in the Eratico patent possesses significant advantages flowing from the simplicity of the retraction mechanism, the writing implement suffers at least one important disadvantage. Specifically, the provision of a small control knob at the end of the implement for controlling extension and retraction of the refill tube makes the implement unwieldy and relatively awkward to handle, particularly as compared with similar implements in which rotation of the cap portion provides the required extension and retraction movements.
A further patent of interest is Italian Pat. No. 518,042 which operates in a similar manner to the Eratico patent discussed above and does provide for extension and retraction of individual ones of three different writing tubes responsive to rotation of a cap. However, in the Italian Patent, the drive cam is located within a hollow housing about which the cap rotates and is attached to a screw element which rotates when the cap is rotated. The hollow housing screws into a support or guide bushing which is mounted in the non-writing end of the barrel of the pen. Thus elements of this arrangement are relatively difficult, and hence expensive, to manufacture and the arrangement is somewhat cumbersome particularly regarding replacement of the writing tubes.
Other patents which disclose extension and retraction mechanisms of interest include U.S. Pat. Nos. 2,865,331 (Marcotte); 3,679,318 (Liguori); and 3,792,931 (Ganz) although this listing is not intended to nor represented to be exhaustive.